1	# rule fuel: a call to a def of the same file, its name then `(`, passes a Nat
2	# literal (`1000n`: digits, then `n`) where that def takes its fuel. A fuel
3	# parameter is known by its name alone (its first lowercase name before the
4	# colon): `fuel`, `gas`, `steps` or `budget`, or any name starting with
5	# `fuel`. The fuel-0 arm returns what it has, so input past the literal comes
6	# out cut short, with no error (a JSON printer that stopped at 1000 tasks).
7	# Inside a law, the checker unrolls the fixed fuel and hangs. Derive the fuel
8	# from the input's size (`Nat.mul(size, 4n)`) or take it as a parameter. A
9	# literal of any size counts, an exact repeat count such as `3n` included.
10	# Only an argument that is one literal token alone counts: `U32.to_nat(1000)`,
11	# a let-bound literal and a parenthesized `(7n)` are not seen. A def's own
12	# calls are exempt: its step passes `fuel - 1`, not a literal.
13	import Base
14	import ../../src.bend as Src
15	import ../../lazy/lazy.bend as Lazy
16	import ../../finding.bend as F
17	import ../../syntax/lex.bend as Lex
18	import ../../syntax/tree.bend as Tree
19	import ../../syntax/bind.bend as Bind
20	import ../calls.bend as Calls
21	import ../tokens.bend as T
22	
23	# a def of the file and the position of a fuel parameter
24	type Fuel is Data:
25	  Fuel{name: String, at: Nat}
26	
27	# is it a fuel parameter's name?
28	def is_fuel(+nn: String) -> Bool:
29	  Bool.or(String.starts_with(nn, "fuel"),
30	    List.contains(~String, ~String.eq, ["gas", "steps", "budget"], nn))
31	
32	# the fuel parameters among a def's parameters, from position i on
33	def fuels.params(ps: List<&2, Tree.Node>, +name: String, +ii: Nat) -> List<&2, Fuel>:
34	  match ps:
35	    case Nil{}:
36	      Nil{}
37	    case Con{p, rest}:
38	      +more = fuels.params(rest, name, 1n+ii)
39	      Bool.pick(List<&2, Fuel>, is_fuel(Calls.param_name(p)), Fuel{name, ii} <> more, more)
40	
41	# every fuel parameter of every def of the file
42	def fuels(ds: List<&2, Calls.Def>) -> List<&2, Fuel>:
43	  match ds:
44	    case Nil{}:
45	      Nil{}
46	    case Con{Calls.Def{name, sig, body}, rest}:
47	      List.append(&2, Fuel, fuels.params(Calls.params(sig), name, 0n), fuels(rest))
48	
49	# an argument that is a Nat literal alone (digits, then `n`), as a finding
50	def literal(aa: Tree.Node, +path: String) -> List<&2, F.Finding>:
51	  match aa:
52	    case Tree.NCons{Tree.Leaf{Lex.Tok{Lex.TNum{}, +t, l, c}}, Tree.NNil{}}:
53	      Bool.pick(List<&2, F.Finding>, T.nat_ok(String.to_list(t)),
54	        [F.Finding{path, l, c, U32.from_nat(String.length(t)), "fuel",
55	          "The fuel is fixed at " ++ t ++ ", so longer input is silently cut short; derive the fuel from the input size."}],
56	        [])
57	    case other:
58	      Nil{}
59	
60	# a call to name with these arguments, against every fuel parameter
61	def call(fs: List<&2, Fuel>, +name: String, +as: List<&2, Tree.Node>, +path: String) -> List<&2, F.Finding>:
62	  match fs:
63	    case Nil{}:
64	      Nil{}
65	    case Con{Fuel{+fn, at}, rest}:
66	      +more = call(rest, name, as, path)
67	      Lazy.stop(List<&2, F.Finding>, Bool.not(String.eq(fn, name)), more,
68	        _u => List.append(&2, F.Finding, literal(Calls.arg(as, at), path), more))
69	
70	# every call at any depth of a chain, but the def's own (self)
71	def calls(nn: Tree.Node, +fs: List<&2, Fuel>, +self: String, +path: String) -> List<&2, F.Finding>:
72	  match nn:
73	    case Tree.NCons{Tree.Leaf{Lex.Tok{k, +t, l, c}}, Tree.NCons{Tree.Group{Lex.Tok{_, +o, _, _}, +kids, _}, rest}}:
74	      +more = List.concat(&2, F.Finding, [calls(kids, fs, self, path), calls(rest, fs, self, path)])
75	      +hit = Bool.and(Bool.and(Lex.is_name(k), String.eq(o, "(")), Bool.not(String.eq(t, self)))
76	      Lazy.stop(List<&2, F.Finding>, Bool.not(hit), more,
77	        _u => List.append(&2, F.Finding, call(fs, t, Calls.args(kids), path), more))
78	    case Tree.NCons{Tree.Group{open, kids, close}, rest}:
79	      List.concat(&2, F.Finding, [calls(kids, fs, self, path), calls(rest, fs, self, path)])
80	    case Tree.NCons{Tree.Stmt{kind, kids, body}, rest}:
81	      List.concat(&2, F.Finding, [calls(kids, fs, self, path), calls(body, fs, self, path),
82	        calls(rest, fs, self, path)])
83	    case Tree.NCons{h, rest}:
84	      calls(rest, fs, self, path)
85	    case other:
86	      Nil{}
87	
88	# a def's (or a law's) name, "" when it has none
89	def own(mm: Maybe<&2, String>) -> String:
90	  match mm:
91	    case None{}:
92	      ""
93	    case Some{n}:
94	      n
95	
96	# each top-level statement, walked as its own def
97	def check.go(root: Tree.Node, +fs: List<&2, Fuel>, +path: String) -> List<&2, F.Finding>:
98	  match root:
99	    case Tree.NCons{Tree.Stmt{kind, +kids, body}, rest}:
100	      +self = own(Bind.declared(kids))
101	      List.concat(&2, F.Finding, [calls(kids, fs, self, path), calls(body, fs, self, path), check.go(rest, fs, path)])
102	    case Tree.NCons{h, rest}:
103	      check.go(rest, fs, path)
104	    case other:
105	      Nil{}
106	
107	# the rule
108	def check(ss: Src.Src) -> List<&2, F.Finding>:
109	  Src.Src{path, text, toks, +tree, bound, items} = ss
110	  check.go(tree, fuels(Calls.defs(tree)), path)